Ultrasound imaging systems have gained wide acceptance for use in providing images of objects and areas which are not otherwise visible to an observer. Such ultrasound imaging systems are typically configured with various imaging parameters selected to produce the best overall ultrasound image quality and not the best visualization of individual objects that may be present in a volume being imaged. As a result, the visualization of individual objects is typically compromised to achieve an overall satisfactory ultrasound image quality.
Objects visualized and represented in ultrasound images may comprise biological structures, such as human tissue and organs, and man-made structures such as implantable devices, instruments, etc. The various biological and man-made structures may require specific imaging parameters to achieve high quality ultrasound visualization of the structures that are different from parameters selected to achieve overall image quality. In addition, the imaging parameters chosen to achieve high quality visualization of one type structure may be significantly different than the parameters chosen to achieve high quality visualization of a different type of structure. Thus, it is not a simple task to provide high quality visualization of one or more individual objects within an overall high quality ultrasound image.
It is now common practice to use ultrasound imaging systems to aid in the guidance and placement of man-made instruments and other objects. For example, interventional instruments, such as needles, catheters, etc., may be used to deliver medication or other fluids directly into a nerve, an artery, or a vein deep within or internal to a patient's body. Such procedures may require precise positioning of an instrument internal to a patient thus requiring high quality ultrasound visualization of both biological structures and man-made instruments.
Using ultrasound imaging systems configured with imaging parameters selected to optimize overall image quality, it is often difficult, and sometimes impossible, to provide adequate visualization of instruments inserted at a steep angle with respect to an ultrasound transducer used to generate an ultrasound image. The problem of poor visualization of instruments inserted at steep angles results, at least in part, from the fact that representations of such instruments in ultrasound images are based on ultrasound echoes that are reflected from the instruments in a specular fashion. The principles of specular reflection indicate that for steep insertion angles the ultrasound echoes reflected from the instruments do not sufficiently intersect the ultrasound transducer elements to produce a clear representation of the instrument in the resulting ultrasound image.
Due to the generally poor representation in ultrasound images of instruments inserted at steep angles, a clinician must often rely on secondary artifacts to visualize or “guess” where the interventional instrument is within a volume (e.g., within a patient's anatomy). For example, a clinician may rely upon movement of tissue, or other structures visible within the resulting image, caused by pressure from a needle as the needle is inserted or otherwise moved, to visualize where the needle is within the patient's anatomy. Visualization of the location of an interventional instrument based upon the movement of nearby structures generally does not provide for precise location determinations.
Another technique used for visualizing the location of an interventional instrument requires injecting fluid through the interventional instrument and observing the resulting image as the fluid moves through the media of the volume being imaged (e.g., as the fluid moves into and through tissue). This technique thus also relies on secondary artifacts and has not been found to be particularly satisfactory.
Several specially-designed echogenic needles have been introduced to address the problem of poor visualization of instruments inserted at steep angles. These specialty needles are typically designed and constructed in a way that the ultrasound waves reflected from the needle reach the ultrasound transducer elements even when the needle is inserted at steep angles. However, there are a number of factors that reduce the effectiveness and desirability of such needles. For example, the increased cost associated with such special needles reduces their clinical acceptance and widespread use.